1. Field of the Invention
The present invention relates to devices for treating fuel vapor, in particular, fuel vapor processors having a canister for trapping fuel vapor (e.g., gasoline vapor), a vapor pipe for leading the fuel vapor from a fuel tank to the canister, a recovery pipe for recovering the fuel vapor trapped in the canister to the fuel tank, a negative pressure generator for generating negative pressure depending on an amount of fuel supplied to the negative pressure generator from a fuel pump disposed in the fuel tank, and a pressure regulator for returning excess fuel discharged from the fuel pump into the fuel tank, the fuel vapor trapped in the canister being recovered into the fuel tank through the recovery pipe due to the negative pressure.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 2002-235608 discloses a fuel vapor processor having a negative pressure generator fluidly communicating with a fuel pump via a pressure regulator. When the fuel pump is running, e.g., during driving, excess fuel discharged from the fuel pump is returned into the fuel tank via the pressure regulator. In this case, the fuel returned from the pressure regulator is led into the negative pressure generator in order to generate negative pressure. This negative pressure generator is provided at the middle of the recovery pipe. And, an open end of the recovery pipe, i.e., an outlet for the fuel vapor recovered from the canister, is submerged in a fuel reserved in the fuel tank. Neither the recovery pipe nor the vapor pipe are equipped with any switching device capable of changing between open and closed states, so that as far as the fuel pump is running and the excess fuel is returned, the fuel vapor processor continuously recovers the fuel vapor.
With respect to such fuel vapor processor, because the negative pressure generator is indirectly communicated with the fuel pump via the pressure regulator, strength of the negative pressure depends on an amount of the excess fuel returned by the pressure regulator. Hence, the strength of the negative pressure varies regardless of a condition of the canister, so that a capability of recovering the fuel vapor is unstable. For example, in a case that a discharge amount from the pump is fixed, when fuel consumption by an engine is high and the return amount by the pressure regulator is low, the strength of the negative pressure is low, so that the capability of recovering the fuel vapor is low. On the other hand, when the fuel consumption by the engine is low and the return amount by the pressure regulator is high, the strength of the negative pressure is high, so that the capability of recovering the fuel vapor is high.
In addition, with respect to the fuel vapor processor, as far as the fuel pump is running and the excess fuel is returned, the fuel vapor is continuously recovered regardless of the amount of the fuel vapor in the canister. Thus, there is a need for improved fuel vapor processors.
Inventors of this application have found that the above-described problem could be solved by direct connection between the negative pressure generator and the fuel pump without the pressure regulator. However, if such direct connection between the negative pressure generator and the fuel pump is applied to the fuel vapor processor disclosed in Japanese Laid-Open Patent Publication No. 2002-235608, another problem occurs. In particular, in a such case that the negative pressure generator and the fuel pump are directly communicated with each other, when the amount of the fuel discharged from the fuel pump is fixed, an amount of the fuel led into the negative pressure generator becomes constant as shown in FIG. 1, so that the strength of the negative pressure is also fixed. Here, a fuel requirement by the engine equals an amount of the fuel supplied to the engine. In this case, the largest amount of the fuel supplied to the engine decreases by the fuel led into the negative pressure generator. If a total amount of the fuel requirement by the engine and the fuel led into the negative pressure generator is lower than a maximum amount of the fuel discharged from the fuel pump, there is no problem. However, when the total amount is larger than the maximum amount of the fuel discharged from the fuel pump as shown by a shaded area in FIG. 1, fuel supplied to the engine would run short.